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Monday, 14 January 2013

At this time of year I am cheered by the thought that although there is very little wildlife to be seen at the moment, everything is just waiting for the moment that is its time to appear: everything is there, but we just can't quite see it.

Hidden plants can be resting as seeds, bulbs, corms or tap roots deep under the ground. Fungi have retreated back to the invisible mycelium which lies below the surface or inside wood. Many warm-blooded mammals and all cold-blooded reptiles and amphibians are hibernating in holes or under the surface of pools, lakes and streams. Molluscs are underground, either as eggs or adults.

But it is insects that have the most varied means of existing through winter. Most insects exist as one of four states: egg, larva, pupa or adult, although some insects - such as bugs - miss out the pupal state and go through a series of nymph stages, and insects can overwinter in each of those four states.

Queen bumblebees - already mated last year - are dormant underground and will emerge in early spring to look for a nesting place to lay the eggs that will become the workers. Similarly, the tiny nests of solitary bees have a small population of pupae that will hatch to create this year's generation. The males are nearer the entrance and will hatch first to establish territories before the females emerge. (This male-first hatching is quite common in insects, presumably to give the males a chance to exercise their fighting and survival skills to ensure stronger future generations. Another example of this is the Orange Tip butterfly, where the males emerge around a week before the females).

We have just under 800 species of micromoth in Ireland, and they overwinter in the widest range of places of any of our species. Some are inside the roots of buttercups; others are inside the seedpods of plants like Gorse; some are inside the stems of grasses, others are inside berries, seeds or fruits. A few leaf miners also make winter mines. Almost any stable or persistent location can be used as overwintering shelter.

Hoverflies overwinter mostly as pupae buried in mud or some other moist substrate such as rotholes in wood, or the roots of thistles, but a few overwinter as mated females ready to emerge when the first sun is around in early spring.

Butterflies also overwinter as pupae, but a few species hibernate as adults and might even be spotted out nectaring in milder days during winter. These overwintering species are the first emergers in spring and will breed to form a summer generation.

Parasitoids, such as ichneumonids, braconids or chalcids will have consumed the host pupae and will have pupated either inside the original pupal case or close by the outside of it. They will emerge when the next generation of host larvae are active and feeding later in the year.

Flies are also quite diverse in their overwintering habits. Some have developed inside the seedheads of flowers such as Knapweed and have pupated there. Others, such as leatherjackets (the larvae of craneflies) are underground after feeding on the roots of grasses.

Few beetles can be seen during winter: most are inside the pupal cases in wood, underground, or inside seedheads.

Tuesday, 8 January 2013

We have a few moths that only emerge once the frosts have arrived. At first glance, this seems to be a flawed plan, since there is little vegetation to support caterpillars and the low temperatures are a hindrance to cold-blooded species (and none of our butterflies have this 'alternative' lifestyle plan). But a bit of investigation reveals that these winter emerging species might actually have a couple of advantages. Firstly, there are no ichneumonids or tachinids around to parasitise them at this time of year. Secondly, there is much less competition for any limited food resources that do exist. Thirdly, the eggs stay inert for a while, so their caterpillars don't hatch until fresh leaves are available, and they pupate before the real competition for summer food arrives. (This early pupation also provides some limited protection from parasites and predators). Furthermore, male moths are generally guided to the female by smell, and the summer moths can travel great distances overnight as they search for a mate, but many (not all) of the winter emerging moths have flightless females that stay in one place after they hatch. This means that the males have much less hunting to do to find a mate, which is a bonus in cold weather. There are some summer-hatching species with flightless females, so it would be interesting to know which came first: the winter hatching or the flightless females. More research, I think.

Here are a couple of winter moths which I photographed in December:

I photographed this very fresh (the abdomen is clearly still pink) Pale Brindled Beauty on the 19th of December, although its normal peak season is in March. This tied in with my sightings of Bumblebees, Celandines, and Willow leaves and catkins all around the same time: all of those would be much more normal in March than December.

Pale Brindled Beauty

I have subsequently discovered that this is the earliest ever date (by one day!) in Ireland for Pale Brindled Beauty to be recorded.

I also saw the very handsome Mottled Umber on December 25th:

Mottled Umber

At first I thought that this was a new species for me, because I had certainly never seen the moth before, but my records show that I had photographed the caterpillar in 2006 (you can see it here). So it's a new adult moth, but not a new species for me.

Both of these moths feed on leaves of a wide range of trees when caterpillars. In each case, the photographs show males, because the females of both species are wingless.

For the last week or so, the wind has been mostly from the south, and I received reports that immigrant moths have been found in the south of the country. I didn't think that they would bother at this time of year: perhaps it's yet another sign of a mild winter to come.